1. Field of the Invention
The present invention relates to a toner, a method of manufacturing the toner, a developer, a two-component developer, a developing device, and an image forming apparatus having the developing device.
2. Description of the Related Art
A toner is used to visualize a latent image in various image forming processes, and one known example thereof is an electrophotographic image forming process.
An electrophotographic image forming apparatus forming images in the electrophotography process is capable of easily forming images with high quality and therefore is widely used for copiers, printers, facsimile machines, and the like equipment.
The electrophotographic image forming apparatus (hereinafter referred to simply as “image forming apparatus”) includes, for example, a photoreceptor, a charging section, a exposing section, a developing section, a transfer section, a fixing section, an electricity removing section, and a cleaning section. The image forming apparatus is an apparatus which uses the photoreceptor and those sections stated above to form an image on a recording medium through a charging step, an exposing step, a developing step, a transferring step, a fixing step, a cleaning step, and an electricity removing step.
In the charging step, a photoreceptor surface is homogeneously charged by the charging section. In the exposing step, the exposing section is used to expose the charged photoreceptor so that an electrostatic latent image is formed on the photoreceptor surface. In the developing step, the electrostatic latent image formed on the photoreceptor surface is developed with use of a toner contained in a developer, and a visualized image is thereby formed. To be specific, the developing section attaches the charged toner to the electrostatic latent image formed on the photoreceptor surface, thereby forming the visualized image on the photoreceptor surface. In the transferring step, the visualized image formed on the photoreceptor surface is transferred by the transfer section onto a recording medium such as paper or a sheet. In the fixing step, the visualized image transferred to the recording medium is fixed thereto with heat or pressure by the fixing section. In the cleaning step, a transfer residual toner remaining on the photoreceptor surface after the transferring step is removed by the cleaning section. In the electricity removing step, the charges in the photoreceptor surface are removed by the electricity removing section to be ready for next image formation. The visualized image may be firstly transferred to an intermediate transfer medium from which the image will be then-transferred to the recording medium.
The developer to be used to form the visualized image includes a two-component developer made of a carrier and a toner, and a one-component developer made of only a toner.
In the two-component developer, the toner and the carrier are mixed with each other to give charges to the toner, and it is therefore necessary to provide a stirring mechanism for mixing the toner and the carrier evenly, which results in a disadvantage that the developing device will have more a complicated structure. The two-component developer however exhibits excellent toner charging stability and compatibility with a high-speed apparatus. This is why the two-component developer is often used in a high-speed image forming apparatus and a color-image forming apparatus.
The one-component developer contains no carrier and therefore does not require the stirring mechanism for mixing the toner and the carrier evenly. The one-component developer therefore has an advantage that a developing device serving as the developing section has a simple structure. However, the toner is charged by friction with a plate-like blade made of metal or resin, which results in a disadvantage that a charge amount of the toner will be barely stable.
In order to enhance the quality of images formed by the image forming apparatus, studies have been made, for example, on the use of the toner having shape-controlled small particles. Such a toner as being composed of shape-controlled particles has however a problem that in the case of forming an image on a rough-surfaced recording medium, the resultant image will have low quality.
The toner contains a release agent, for example, to prevent an offset phenomenon that the toner on the recording medium adheres to the fixing section in the fixing step. In forming an image, the release agent existing in a surface of the toner become more soluble as an internal temperature of a developing tank rises by rotation of a developing roller in the developing tank, and the release agent exposed on the surface of toner becomes a center of adherence of the toner to a charge applying material which is, for example, a carrier in the case of the two-component developer, or a regulating blade in the case of the one-component developer. Further, the heat of the fixing device also increases the internal temperature of the developing tank. The above adherence is higher as the developer is exposed to a high temperature for longer hours and as a larger area of the release agent exposed on the surface of the toner makes contact with the charge applying material.
As described above, when the amount of the release agent exposed on the surface of toner increases due to the shape control of toner particles, the toner and carrier in the developer will start to aggregate from the part of release agent exposed on the surface of toner, and such aggregation will deteriorate flowability of the developer, or will cause the release agent to be fused and fixed to the regulating blade. In this state, the toner consequently exhibits a lower developing property and thus forms images with lower quality. Especially for the rough-surfaced recording medium to which images are less smoothly transferred than a smooth-surface recording medium, images formed on such rough-surface recording mediums will have still lower quality.
In order to solve the above problems, Japanese Unexamined Patent Publication JP-A 9-319158 (1997) discloses a developer consisting of a carrier and a toner, the carrier being composed of a core material and a resin-coating layer deposited on the core material, the resin-coating layer having dispersion of resin fine particles of melamine, guanamine, or the like resin containing nitrogen atoms, and the toner containing a binder resin, a colorant, and wax, wherein an amount of the wax exposed on a surface of toner is 15% by weight to 40% by weight, and wherein 40≦X×Y≦240 is satisfied where X represents an amount of the wax exposed on the surface of toner and Y represents an amount of the wax contained in the toner. According to JP-A 9-319158, it is possible to obtain an electrostatic latent image developer having good flowability and a very long life with less environmental dependency, which developer is capable of reducing toner spent to the carrier, toner blocking, or fusing onto the regulating blade, and able to be fixed over a broad temperature range.
Further, Japanese Unexamined Patent Publication JP-A 2008-20578 discloses an electrostatic charge image developing toner containing toner base particles containing a binder resin and a release agent as well as one or more external additives, wherein according to the X-ray photoelectron spectroscopy (abbreviated as XPS) quantification, the release agent exposed on surfaces of toner base particles accounts for 10% to 40%, and in the surfaces of the toner base particles, the external additive present on a release agent part accounts for 15% or less while the external additive present on the other parts than the release agent part accounts for 20% or more and 100% or less. According to JP-A 2008-20578, it is possible to obtain the electrostatic charge image developing toner which achieves a balance between its favorable powder flowability and its favorable fixing property causing no such troubles as hot offset.
However, in the toner contained in the electrostatic latent image developer disclosed by JP-A 9-319158, the amount of the wax exposed on the surface of the toner is too large to sufficiently curb the increase in the adherence of the toner to the carrier caused by the internal temperature rise of the developing tank, and it is therefore difficult to sufficiently prevent the flowability of the developer from deteriorating. Besides, the recent downsizing and speeding-up trend of image forming apparatus causes a further rise in the internal temperature of the developing tank, which leads to a more obvious decline in the flowability of the developer.
In the electrostatic charge image developing toner disclosed by JP-A 2008-20578, the external additive present on the release agent part in the surfaces of the toner base particles is defined, but the percentage of the release agent exposed on the surfaces of the toner base particles is too high to sufficiently curb the increase in the adherence of the toner to the carrier caused by the internal temperature rise of the developing tank, and it is therefore difficult to sufficiently prevent the flowability of the developer from deteriorating. Besides, the recent downsizing and speeding-up trend of image forming apparatus causes a further rise in the internal temperature of the developing tank, which leads to a more obvious decline in the flowability of the developer.